initializeData attribute controls where the trace log file is saved. Now when you execute a package inside Visual Studio, "c:\System.Net.trace.log" file will contain the web services tracing information. If you want to trace when you execute packages outside Visual Studio, include the settings above in DTExec.exe.config configuration file.

Make sure you comment or remove the tracing settings after you finish testing. Otherwise this may slow down your package execution speed considerably.